Add two Principled BSDF with alpha
If I understood your question, you have to combine two different materials into one, using the alpha channel to mix between the two shaders.

In my example I created a material for all the faces except the zone of the logo, then duplicated it, assigned the dupli version to the faces of the logo zone, then added in the dupli version a new principled shader, with the image as base color.

Then I used alpha channel to mix between the two shaders.